Toxic Soup

How dangerous is running on high-pollution days?

This article originally appeared in our September 2013 issue.

In 2008, then marathon-world-record holder, Haile Gebrselassie of Ethiopia, decided not to run in the Beijing Olympics. Even though he would only be running for just over two hours, Beijing’s air pollution and its attendant risk of long-term damage outweighed the prospect of a probable Olympic Medal.

To run or not to run? This is a question many of us living in the polluted pools of our cities ask ourselves on a daily basis. We’ve been peeing in the pool for so long now that the World Health Organization attributes nearly one-million deaths per year to inhaling polluted air.

In the 1990s, Brigham Young University economics professor C. Arden Pope’s research found that higher levels of tiny particles in the air are associated with increased mortality rates. Air pollution has been shown to worsen respiratory issues, and cause cardiovascular damage (leading to heart attacks, strokes and heart disease) and infants to have lower birth weights.

What Pollutes Our Air?

The atmospheric layer closest to Earth is called the troposphere. It contains the air we breathe. Human activities, from vehicle exhaust to industrial emissions, create the two biggest concerns for our health: ground- level ozone and particulate matter.

Ground-level ozone occurs when engine and fuel gases in the air react in the presence of heat and sunlight. Ozone levels increase in cities when the air is still, the sun is bright and the temperature is warm. Ozone is therefore worse in the summer because of the ripe conditions.

Particulate matter is a general term describing microscopic particles floating in the air. The particles are so small they can only be seen with an electron microscope; however, when a lot of them are present, you get a visible blanket of smog, e.g. the kind you see in Salt Lake City during a winter inversion.

When you run you breathe in huge volumes of air—10 to 20 percent more than someone sitting on the couch—exposing you to greater levels of pollutants. The pollution penetrates deep into the lungs, where it creates inflammation and oxidative stress (a harmful byproduct of your cells producing energy), and can contribute to conditions such as asthma and chronic obstructive pulmonary disease. That's why, during high-pollution summer days, you may hear warnings about not exercising outdoors.